The project seeks to study cellular compartmentation as a biochemical regulatory factor. It has two parts. 1. The enzyme carbamyl phosphate synthetase A of the fungus Neurospora participates in arginine synthesis and is located in the mitochondria. It is made of two different protein subunits. We will study the subunit structure, the process of subunit aggregation, the regulation of each subunit, and the insertion of enzyme into the mitochondrion. In these studies, we wish to determine the role of each factor in the control of enzyme activity in the cell. 2. Basic amino acids are sequestered in "vesicles" in the cells of Neurospora, and serve as a reservoir and regulator of cytoplasmic concentrations of these compounds. We wish to characterize in more detail the physical properties, the contents, and the accumulation mechanism of the isolated and purified vesicles. The information gained in both parts of the project are applicable to mammalian cells, which have similar compartmental phenomena in the arginine pathway.